This invention relates to systems and methods for fabricating molecular electronic devices.
Many different molecular electronic logic and memory devices have been proposed.
For example, in one molecular electronic device structure, a molecular layer (e.g., a Langmuir-Blodgett film) is sandwiched between a pair of electrically conducting layers (e.g., a pair of metal layers, a metal layer and a doped semiconductor layer, or a pair of doped semiconductor layers). The molecular layer serves as a thin insulating film that may be used in a metal-insulator-metal (MIM) structure that may be configured as a tunnel junction device or a switching device, or a metal-insulator-semiconductor (MIS) structure that may be configured as an electroluminescent device.
U.S. Pat. No. 6,128,214 describes another molecular electronic device structure that is configured as a molecular wire crossbar memory (MWCM) system formed from a two-dimensional array of nanometer-scale devices. Each MWCM device is formed at the crossing point (or junction) of a pair of crossed wires where at least one molecular connector species operates as a bi-stable molecular switch between the pair of crossed wires. The resulting device structure may be configured as a resistor, a diode or an asymmetric non-linear resistor. The state of each MWCM device may be altered by applying a relatively high, but non-destructive, state-changing voltage and may be sensed with a non-state-changing voltage.
Still other molecular electronic devices have been proposed.
The invention features a novel process of fabricating a molecular electronic device that preserves the integrity of the active molecular layer of the electronic device during processing. In addition, the invention features a novel molecular electronic device structure and a novel memory system that are formed with this fabrication process.
In one aspect, the invention features a method of fabricating a molecular electronic device in accordance with which a barrier layer is provided to protect a molecular layer, which is sandwiched between a bottom wire layer and a top wire layer, from degradation during patterning of the top wire layer.
Embodiments of the invention may include one or more of the following features.
The molecular layer and the top wire layer preferably have a combined thickness that is less than the barrier layer thickness in a region defining the molecular electronic device.
The top wire layer preferably is patterned by disposing a lift-off layer over the barrier layer, disposing an electrically conductive layer over the molecular layer and the lift-off layer, and dissolving the lift-off layer. The lift-off layer preferably has a different solubility characteristic than the barrier layer. The lift-off layer preferably is dissolved with a solvent with respect to which the barrier layer is substantially insoluble. In some embodiments, the lift-off layer may comprise a polymer (e.g., PMMA) and the barrier layer may comprise a different polymer (e.g., PDMS). In these embodiments, the lift-off layer may be dissolved in acetone. In other embodiments, the lift-off layer may comprise a polymer and the barrier layer may comprise an inorganic electrical insulator.
In another aspect of the invention, a molecular electronic device is fabricated as follows. A patterned bottom wire layer is disposed over a substrate. A composite layer, which includes a lift-off layer and an underlying barrier layer, is disposed over the patterned bottom wire layer. The composite layer is patterned to define a device region in which the bottom wire layer is exposed through the lift-off layer and the barrier layer. A molecular layer and an overlying top wire layer are disposed over the patterned composite layer and the exposed bottom wire layer. The molecular layer and the top wire layer have a combined thickness in the device region that is less than the thickness of the barrier layer defining the device region. The top wire layer is patterned by dissolving the lift-off layer with a solvent with respect to which the barrier layer is substantially insoluble.
The invention also features a molecular electronic device that includes a bottom wire layer, a molecular layer disposed over the bottom wire layer in a device region, a top wire layer disposed over the molecular layer in the device region, and a barrier layer. The barrier layer defines the device region and has a thickness that is greater than a combined thickness of the molecular layer and the top wire layer.
In another aspect, the invention features a molecular memory system comprising an array of devices corresponding to the molecular electronic device described in the preceding paragraph.
Other features and advantages of the invention will become apparent from the following description, including the drawings and the claims.